Fatty liver disease is a condition characterized by excessive accumulation of lipids (fat) in liver. The build-up of fat in liver results in a range of clinical manifestations and progresses in stages. Depending on etiology, each stage can be characterized as non-alcoholic or alcoholic. The progression begins with simple fatty liver, or steatosis. This stage, generally regarded as benign, is characterized by the increased appearance of fat in the liver. Fatty liver can be characterized as non-alcoholic (NAFL) or alcoholic (AFL). The next stage of a fatty liver disease is a form of hepatitis known as steatohepatitis, characterized by further fat accumulation and liver tissue inflammation. Steatohepatitis can be non-alcoholic (NASH) or alcoholic (ASH). Both NASH and ASH can lead to the next stage of fatty liver disease, NASH-associated or ASH-associated fibrosis, respectively, which is characterized by scarring of the liver. Finally, fibrosis can progress to cirrhosis, which causes irreversible damage to the liver and is the most severe stage. Cirrhosis can be non-alcoholic or alcoholic.
Common risk factors for fatty liver disease are obesity, diabetes and drinking alcohol to excess. While the relationship between these factors is not fully understood, they can be considered triggers for progression of the disease.
People most at risk of the disorders caused by fat accumulation in a liver are those who:                are obese        have insulin resistance, associated with diabetes        have hypertension (high blood pressure)        have hyperlipidemia (too much cholesterol and triglyceride in their blood)        are taking certain drugs prescribed for other conditions        have been malnourished, starved or given food intravenously.        
Diseases caused by fat accumulation over time should be distinguished from acute fatty liver disease, which may occur during pregnancy or with certain drugs or toxins (poisons). This condition is very rare and may lead rapidly to liver failure.
There are currently no suitable agents for treating simple fatty liver disease and its progressive stages (e.g. NASH and ASH). Therefore, there is an urgent need for the treatment of this disease.